Evaluating and Improving Urban Drainage Capacities in China (PAP014360)
Hong Wang, Xiaotao Cheng
Urban floods are increasingly witnessed in China due to the imbalance between rapid urbanization and outdated structural and non-structural measures in urban drainage and flood risk management. In recent years, China has directed its attention to urban floods and began to shift its urban flood management policies from separating city drainage and fluvial flooding to an integrated, more holistic and sustainable approach indicating a notable progress. But the overall drainage capacities in urban areas still lag behind the modern world. A recent survey shows that the drainage capacities in most Chinese cities are ranging from 1- to 3-year return period based on the conventional Chinese design method. To address urgent challenges of urban floods, pressing demands have arisen for more accurate and feasible approaches to evaluate and improve existing urban drainage systems and move forward to more cost-effective and environmental-harmonious urban drainage nationwide. This research investigates whether the conventional urban drainage design method, widely used in China for over half a century, are appropriate for modern drainage design by examining basic design concepts from rainfall-intensity-frequency estimation, peak runoff calculation to drainage system integration. To facilitate a better understanding of the discrepancy between China's conventional design method and advanced design techniques based on new knowledge and technology, a hypothetical case study is conducted utilizing both conventional Chinese design method and a more detailed hydrologic-hydraulic modeling technique using USEPA's computer program, SWMM. The results show that comparing to the conventional Chinese design method, the capacity of the case-study drainage system increased from a 3-year return period to a 7-year return period using SWMM modeling technique. Aimed to further improve the drainage capacities in Chinese cities, variety of sustainable measures are considered in the hypothetical case study. In general, infiltration measures are utilized to diminish the first 25mm rain; storage measures are implemented to capture the next 25mm rain; gravel-lined or vegetated channels and other waterways are adapted to increase runoff travelling times. After applying various sustainable measures, an existing drainage system, which was estimated to drain a 3-year event by conventional Chinese design method, will be able to sustain a 20-year storm event without replacing large amount of existing sewers.